Cardiac pacing electrically stimulates the heart when the heart's natural pacemaker and/or conduction system fails to provide synchronized atrial and ventricular contractions at appropriate rates and intervals for a patient's needs. Such bradycardia pacing provides relief from symptoms and even life support for hundreds of thousands of patients. Cardiac pacing may also give electrical overdrive stimulation intended to suppress or convert tachyarrhythmias, again supplying relief from symptoms and preventing or terminating arrhythmias that could lead to sudden cardiac death.
A temperature sensor can detect changes in a patient's blood temperature, which varies with exercise. Although certain conventional pacemakers in the past used temperature-based activity sensors to enable an increase in pacing rate in response to exercise, as described in U.S. Pat. No. 5,005,574 to Fearnot and U.S. Pat. No. 4,543,954 to Cook, each of which is incorporated herein by reference in its entirety, current conventional pacemakers generally use an accelerometer-based activity sensor to provide a rate response. Temperature-based rate response leadless pacemakers are described in U.S. Pat. No. 7,937,148 to Jacobson, U.S. Pat. No. 8,543,205 to Ostroff, and U.S. Pub. No. 2013/0261497 to Pertijs, each of which is incorporated herein by reference in its entirety. Jacobson describes a leadless cardiac pacemaker containing a rate-response temperature sensor hermetically contained within the pulse generator housing. Ostroff demonstrates response times for sensing changes in blood temperature with the temperature sensor mounted in various locations within the pulse generator. Pertijs describes a leadless pacemaker using a semiconductor temperature sensor supported by the housing.